The present invention relates to a method for operating a purification device for gases, especially for exhaust gases of stoichiometrically operated gasoline engines, wherein a filter body comprising a catalyst is exposed to a gas stream to catalytically convert pollutants, as well as to a purification device for gases comprising a filter body which comprises a catalyst, particularly for stoichiometrically operated gasoline engines, wherein the filter body is disposed in the exhaust gas stream of an engine, wherein both the method and the purification device are useful in the automobile industry.
In the past, to improve the cold-running properties and, in particular, to reduce hydrocarbon emission in the exhaust gases of motor vehicles with a controlled exhaust gas catalyst, the catalyst was generally heated in the starting phase. This requires additional energy and an increased weight. Moreover, such a purification device is expensive and difficult to recycle because of the catalysts used, such as noble metals and the like.
Published German Patent 44 20 932 discloses a catalyst for an exhaust gas purification device. This catalyst is made of a spinel or a spinel-like composition and is particularly useful for gasoline engines and/or diesel engines operated on a lean mixture. Among other things, the catalyst has a high resistance to substances present in the exhaust gas. Furthermore, the catalyst acts in an oxidizing manner with carbon monoxide and hydrocarbons and in a reducing manner with NO.sub.x, particularly with NO and NO.sub.2.
It is an object of the present invention to improve the method as well as the purification device to improve the purifying effect during the starting phase.
According to the present invention, this and other objectives are accomplished by a method comprising the steps of
at temperatures below the response temperature of the catalytic material contained in the purification device, particularly at temperatures below 200.degree. C. and preferably at temperatures below 150.degree. C., storing hydrocarbons present in the gas in the filter body, PA1 at temperatures above the response temperature, releasing the hydrocarbons and PA1 catalytically converting pollutants with the support material of the filter body.
The present invention furthermore relates to a purification device comprising a filter body of catalytic material which stores at least 20% by volume, preferably at least 50% by volume, of hydrocarbons at temperatures below the response temperature of the catalytic material, particularly at temperatures below 200.degree. C., preferably below 150.degree. C., wherein the catalytic material, with the help of a reducing agent which is preferably hydrocarbon and/or carbon monoxide, catalytically reduces pollutants.
By using a catalytically-active support material, which also acts as a storage medium for hydrocarbons at temperatures below the catalytic response temperature of the purification device, that is, at the temperature at which the catalytic reduction and/or oxidation of pollutants, particularly the catalytic reduction of NO.sub.X and the catalytic oxidation of CO takes place, it is possible to eliminate heating of the catalyst in the starting phase. Furthermore, hydrocarbons present in the exhaust gas can also be used as a reducing agent for the nitrogen oxides, especially for NO and NO.sub.2, as a result of which the amount of these gases in the exhaust gas can be lowered. Moreover, because of the catalytic activity of the support material, the need for expensive catalysts, such as noble metals, rare earth metals, lanthanide, etc. can be reduced as a result of which the purification device becomes less expensive.
These and other objects, features and advantages will become more apparent from the following detailed description of presently preferred embodiments when taken in conjunction with the accompanying drawings.